1. Immunization experiments performed on mice with various vaccines
prepared from S. dublin and other Salmonella species showed that a formalinized
aluminium hydroxide precipitated vaccine gave the best protection against virulent
cultures of S. dublin. The immunity produced gave only a partial or incomplete
protection, yet when this vaccine was used for the routine immunization of calves
on badly infected premises in different parts of the country a marked reduction
in deaths from paratyphoid was effected. In a few outbreaks where the routine
vaccine failed to prevent losses a vaccine made from a local strain of S. dublin
invariably gave complete protection against natural exposure. But unless the
vaccine was employed regularly and all the calves born on the farm were
inoculated soon after birth, losses continued to occur. In a few cases where
the use of the vaccine was discontinued fresh outbreaks of paratyphoid usually
In spite of the excellent results obtained with vaccine in the field, it is
admitted that the immunity produced is of a low grade and that it cannot be
relied upon entirely to prevent symptoms or even death from paratyphoid. When
the immunity in calves was challenged with fresh milk-cultures given by the
mouth the majority of them reacted and developed symptoms of paratyphoid,
although much less severely than the control calves.
2. The immunization of calves with routine S. dublin vaccine resulted in the
production of "H" agglutinins almost exclusively. Whereas the "H" agglutinin
titre of the serum of the vaccinated animals rose from 1:25 or less to 1:3,200
or more after immunization, there was hardly any perceptible "0" agglutinogenic
response in the majority of these animals, and the "0" titre remained extremely
low in all of them.
When the immunity was boosted by means of a third injection of vaccine
30 days after the second a very marked rise in the "H" agglutinin titre resulted,
but there was only a slight "0" agglutinogenic response in some of the animals
and hardly any "0" agglutinins could be detected in the others.
3. An easy method of artificially infecting calves with fresh milk cultures
of S. dublin is described. By the utilization of this method the pathogenesis and
the course of the disease could be observed and treatment instituted. It was
found that when calves manifesting typical symptoms of paratyphoid were treated
with large doses of phthalylsulphathiazole by the mouth recovery supervened,
whereas untreated calves, infected in the same way and left as controls, died.
Phthalylsulphathiazole can, therefore, be regarded as an effective therapeutic
agent for calf paratyphoid, and its employment can be recommended for the
treatment of this disease.
It was observed subsequently, however, that fresh milk-cultures of the same
strain of S. dublin, grown under apparently identical conditions, might not always
be equally pathogenic for calves. Sometimes an acute and fatal disease was set
up, whereas, at other times, very much milder symptoms were produced. Although
the cause of this variation is not known it is believed that some factor in the
media is responsible.